Add version

README.md

@@ -1,3 +1,23 @@
 # beam
 
-File transfer service via http
+File transfer service via http.
+
+## Versioning
+
+The Dockerfile owns the base application version with the `VERSION` build argument. Docker builds append the current git short hash with `GIT_SHA` so the homepage can display the exact image version near the bottom-left edge.
+
+```sh
+./build.sh
+```
+
+To push `docker.sdal.tech/beam:latest` after building:
+
+```sh
+./build.sh push
+```
+
+Local non-Docker builds display `vdev` unless a version is injected manually:
+
+```sh
+go build -ldflags "-X main.version=0.1.0-dev" -o beam .
+```